Field of the Invention
The ability to isolate DNA sequences coding for naturally-occurring polypeptides and introducing the isolated sequences into foreign hosts for expression of the encoded polypeptide has greatly expanded the opportunities to produce polypeptides or analogs thereof having biological activity. As more is learned about the mechanism of expression in both prokaryotes and eukaryotes, there is an expanding appreciation of the sophistication of the mechanisms of transcription and translation, as well as replication, and the interaction of naturally-occurring segments, both coding and non-coding. While various techniques have been developed which aid in the isolation, sequencing and synthesizing of DNA and peptides, each investigation of expression of a new polypeptide frequently results in unanticipated obstacles, which require new approaches or modifications of existing techniques.
It has long been known that B. thuringiensis species produce a variety of proteins having insecticidal activity. Because of their natural nature, biodegradability, and the apparent absence of insect resistance to their toxicity, these insecticides have attracted much interest. However, due to the difficulties of growing the host for producing the insecticidal protein, the use of these naturally-occurring insecticides has been somewhat limited. It has therefore become of interest to develop DNA sequences coding for proteins having the same or analogous properties to the naturally-occurring B. thuringiensis insecticides.